Age-dependent changes of ultrastructure and thyroid-stimulating hormone immunoreactivity in the pars tuberalis of the rat.

The pars tuberalis of the rat adenohypophysis was investigated by immunohistochemistry and electron microscopy at different stages of the peri- and postnatal development. A characteristic pattern of changes in thyroid-stimulating hormone immunoreactivity of pars tuberalis-specific secretory cells was observed with an increase in staining intensity after birth, a marked reduction in adulthood and a subsequent increase in senium. Electron microscopy showed age-dependent changes in the number of dictyosomes per cell, in the number of large lysosomes per area of cytoplasm and in the extension of the granular endoplasmic reticulum. The number of secretory granules per area of cytoplasm was maximal perinatally; there was no correlation between granule content and immunoreactivity. Thyrotropes of the pars distalis did not show comparable immunohistochemical or ultrastructural changes.